In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, carbon dioxide CO2. With increasing environmental demands various processes for removing carbon dioxide from the process gas have been developed. One such process is the so called oxy-fuel process. In an oxy-fuel process a fuel, such as one of the fuels mentioned above, is combusted in the presence of a nitrogen-lean gas. Oxygen gas, which is provided by an oxygen source, is supplied to a boiler in which the oxygen gas oxidizes the fuel. In the oxy-fuel combustion process a carbon dioxide rich flue gas is produced, which can be disposed of in order to reduce the emission of carbon dioxide into the atmosphere.
An example of an oxy-fuel boiler is described in US 2007/0243119. The oxy-fuel boiler of US 2007/0243119 generates a process gas which is referred to as a flue gas. A gas cleaning system comprising various gas cleaning devices are utilized for cleaning the flue gas from, among other things, particulate material and sulfur dioxide, to obtain a gas which is suitable for being disposed of. A problem with the gas cleaning system and method of cleaning a gas disclosed in US 2007/0243119 is the rather high operating costs.